Abstract:

Provided is an abnormality detecting device for detecting an abnormality
of electric storage devices such as a battery pack. Comparators (140-1)
to (140-n) detect a time when a voltage reaches a prescribed voltage, for
each block of a battery pack (100). A judging section (160) detects a
current at a time when the voltage reaches the prescribed voltage, and a
representative current value is calculated for each block. The deviation
of the representative current value of each block is compared with the
threshold value, and when the deviation is large, it is judged that there
are abnormalities such as short-circuiting, minute short-circuiting, IR
(internal resistance) increase, capacitance reduction, and the like.

Claims:

1. A detecting device which detects abnormality of an electric storage
device having a plurality of blocks which are connected in series, each
block having one or a plurality of electric storage units, the detecting
device comprising:a measurement unit which measures, for each block, a
current value at a time when a voltage of the block becomes equal to a
predetermined voltage; anda detecting unit which detects abnormality of
the electric storage device based on a deviation of the measured current
value of each block.

2. The abnormality detecting device for an electric storage device
according to claim 1, whereinthe detecting unit comprises:a calculating
unit which calculates a representative current value of each block
through a predetermined statistical process based on a plurality of the
measured current values of each block; anda comparing unit which compares
a deviation of the calculated representative current value of each block
with a predetermined value to detect abnormality of the electric storage
device.

3. The abnormality detecting device for an electric storage device
according to claim 2, whereinthe representative value is one of an
average value, an intermediate value, a minimum value, and a maximum
value of the plurality of the current values of each block.

4. The abnormality detecting device for an electric storage device
according to claim 1, whereinthe detecting unit detects, as the
abnormality, at least one of short-circuiting, increase in internal
resistance, and reduction in capacitance.

5. The abnormality detecting device for an electric storage device
according to claim 1, whereinthe electric storage device is one of a
battery and a capacitor.

6. A method of detecting abnormality of an electric storage device having
a plurality of blocks which are connected in series, each block having
one or a plurality of electric storage units, the method comprising the
steps of:measuring, for each block, a current value at a time when a
voltage of the block becomes equal to a predetermined voltage;
anddetecting abnormality of the electric storage device by comparing a
deviation of the measured current value of each block with a threshold
value.

7. A computer-readable recording medium storing a computer program for
detecting abnormality of an electric storage device having a plurality of
blocks which are connected in series, each block having one or a
plurality of electric storage units, which, when executed, causes a
computer to execute a process comprising:measuring, for each block, a
current value at a time when a voltage of the block becomes equal to a
predetermined voltage;sequentially storing the measured current value of
each block in a memory;causing a calculating device to calculate a
representative current value of each block through a predetermined
statistical process based on a plurality of the current values of each
block stored in the memory;causing the calculating device to calculate a
deviation of the representative current value of each block obtained
through the calculation; anddetecting abnormality of the electric storage
device by comparing in size the deviation obtained through the
calculation and a threshold value.

8. The abnormality detecting device for an electric storage device
according to claim 1, whereinas the predetermined voltage, at least two
predetermined voltages including a first predetermined voltage and a
second predetermined voltage are set; andthe detecting unit detects the
abnormality of the electric storage device based on a deviation of the
current value of each block at a time when the voltage becomes equal to
the first predetermined voltage and a deviation of the current value of
each block at a time when the voltage becomes equal to the second
predetermined voltage.

9. The abnormality detecting device for an electric storage device
according to claim 1, whereinthe measurement unit measures a current
value having a time lag within 100 msec as the current value at the time
when the voltage of the block becomes equal to the predetermined voltage.

10. The abnormality detecting device for an electric storage device
according to claim 2, whereinthe calculating unit extracts only a current
value within a predetermined range from among the plurality of measured
current values of each block and calculates the representative value of
each block through the predetermined statistical process.

11. The abnormality detecting device for an electric storage device
according to claim 2, whereinthe calculating unit calculates the
representative current value only for a plurality of current values
having a distribution degree of a predetermined value or less, among the
plurality of measured current values of each block.

12. A detecting device which detects abnormality of an electric storage
device having a plurality of blocks which are connected in series, each
block having one or a plurality of electric storage units, the detecting
device comprising:a measurement unit which measures a current value at a
time when a voltage difference between adjacent blocks among the
plurality of blocks becomes equal to a predetermined voltage; anda
detecting unit which detects abnormality of the electric storage device
based on a size of the measured current value.

13. The abnormality detecting device for electric storage device according
to claim 12, whereinthe detecting unit detects, as the abnormality, at
least one of short-circuiting, increase in internal resistance, and
reduction of capacitance.

14. The abnormality detecting device for electric storage device according
to claim 12, whereinthe electric storage device is one of a battery and a
capacitor.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a device, a method, and a program
for detecting abnormality of an electric storage device, and in
particular, to a technique for detecting abnormality of an electric
storage device such as a battery pack which comprises a plurality of
blocks connected in series.

BACKGROUND ART

[0002]In the related art, a battery pack in which a block is constructed
by connecting one or a plurality of batteries in series and a plurality
of the blocks are connected in series is equipped in a hybrid automobile
and an electric automobile, and a device for measuring voltage or current
of each block of the battery pack and detecting abnormality has been
developed. A basic method of detection of the abnormality is that a
voltage and a current are measured for each block and an internal
resistance (IR) is calculated through the method of least squares. The
abnormality is detected based on an increase or a deviation of IR.

[0003]FIG. 12 shows a result of a plot of current against voltage for a
block obtained through measurement, with the horizontal axis representing
the current and the vertical axis representing the voltage (block
voltage). In FIG. 12, the X mark represents each measurement point. A
straight line 50 is a straight line obtained by the method of least
squares based on the plurality of measurement points, and the slope of
the straight line represents the IR. For each block of the battery pack,
a straight line is calculated, and when the straight lines are in an
allowable range, the battery pack is determined to be normal. On the
other hand, as shown in FIG. 13, when a straight line 60 of a certain
block has a large deviation with respect to the straight lines 50 of the
other blocks when the straight lines are calculated through the method of
least squares for each block, the abnormality of the battery pack is
detected by determining that IR has increased due to elapse of the
lifespan, compromising of airtightness, etc.

[0004]JP 2001-196102 A discloses a technique of detecting abnormal
increase in temperature of the battery in which the IR of each block is
calculated based on the block voltage and the current and the IR is
compared with a predetermined threshold value. FIG. 14 shows a structure
of the battery pack control device disclosed in this reference. The
battery pack control device is equipped in a hybrid automobile. The
battery pack control device controls input and output of a battery pack
10. The battery pack 10 comprises a plurality of blocks 10A which are
connected in series. Each of the plurality of blocks 10A comprises a
plurality of single batteries 10B which are connected in series. The
battery pack control device comprises a battery power input and output
section 1 which controls an input and an output of power of the battery
pack 10, a block voltage detecting section 2 which detects a block
voltage of each of the plurality of blocks 10A, a battery current
detecting section 3 which detects a battery current of the battery pack
10, an abnormal temperature increase detecting section 4 which detects
abnormal temperature increase of the single battery 10B based on the
block voltage and the battery current, a vehicle control section 5 which
controls the battery power input and output section 1 based on a
detection result of abnormal temperature increase by the abnormal
temperature increase detecting section 4, and a battery temperature
detecting section 6 which detects a battery temperature of the battery
pack 10. The abnormal temperature increase detecting section 4 comprises
an internal resistance calculating section 4A which calculates an
internal resistance of each of the plurality of blocks 10A based on the
block voltage and the battery current, a threshold value setting section
4B which sets a threshold value based on the battery temperature of the
battery pack 10, a variance calculating section 4C which calculates an
average value and a variance σ2 of the block voltage of each
of the plurality of blocks 10A, a variance abnormal temperature increase
detecting section 4D which detects an abnormal temperature increase of
the single battery 10B based on the block voltage, average value, and
variance σ2 of each of the plurality of blocks 10A, and a
remaining capacitance abnormal temperature increase detecting section 4E
which detects abnormal temperature increase of the single battery 10B
based on a remaining capacitance of each of the plurality of blocks 10A.
The battery power input and output section 1 comprises an inverter 1A of
a hybrid automobile and a motor generator 1B. The motor generator 1B
drives an engine 12 through a transmission 11. An engine control section
13 controls the engine 12 based on an output of the vehicle control
section 5. The vehicle control section 5 is connected to an acceleration
pedal 7, a braking pedal 8, a shift lever 9, and a battery remaining
capacitance detecting section 14. The vehicle control section 5 controls
the battery power input and output section 1 based on a detection result
of the abnormal temperature increase by the abnormal temperature increase
detecting section 4.

[0005]JP 2005-195604 A discloses a technique in which a voltage of each of
a plurality of batteries of a battery pack is measured at a predetermined
time and the current flowing through the battery pack is measured at the
same time, a difference between the maximum value and the minimum value
of each voltage obtained through the measurement is calculated, and the
abnormality of the battery pack is detected based on values of the pair
of the current and the difference.

[0006]However, in the structure of measuring the block voltage and the
current for each block, an A/D conversion is required for the block
voltage, which may result in an increase in the cost. In addition,
because the IR is calculated through the method of least squares based on
the block voltage and the current, there is a problem in that the
processing time is increase and the load of the processing program is
increased due to the increase in the amount of calculation. In addition,
when the speed of the calculation is increased in such a state, heat
generation may result, which may prevent size reduction of the detection
device.

DISCLOSURE OF INVENTION

[0007]The present invention provides a device and method which can quickly
and accurately detect abnormality of an electric storage device such as a
battery pack and a capacitor, with a simple structure.

[0008]According to one aspect of the present invention, there is provided
a detecting device which detects abnormality of an electric storage
device having a plurality of blocks which are connected in series, each
block having one or a plurality of electric storage units, the detecting
device comprising a measurement unit which measures, for each block, a
current value at a time when a voltage of the block becomes equal to a
predetermined voltage, and a detecting unit which detects abnormality of
the electric storage device based on a deviation of the measured current
value of each block.

[0009]According to another aspect of the present invention, there is
provided a method of detecting abnormality of an electric storage device
having a plurality of blocks which are connected in series, each block
having one or a plurality of electric storage units, the method
comprising the steps of measuring, for each block, a current value at a
time when a voltage of the block becomes equal to a predetermined
voltage, and detecting abnormality of the electric storage device by
comparing a deviation of the measured current value of each block with a
threshold value.

[0010]According to another aspect of the present invention, there is
provided a recording medium storing a computer program for detecting
abnormality of an electric storage device having a plurality of blocks
which are connected in series, each block having one or a plurality of
electric storage units, which, when executed, causes a computer to
execute a process comprising measuring, for each block, a current value
at a time when a voltage of the block becomes equal to a predetermined
voltage, sequentially storing the measured current value of each block in
a memory, causing a calculating device to calculate a representative
current value of each block through a predetermined statistical process
based on a plurality of current values of each block stored in the
memory, causing the calculating device to calculate a deviation of the
representative current value of each block obtained through the
calculation, and detecting abnormality of the electric storage device by
comparing in size the deviation obtained through the calculation and a
threshold value.

[0011]According to another aspect of the present invention, there is
provided a detecting device which detects abnormality of an electric
storage device having a plurality of blocks which are connected in
series, each block having one or a plurality of electric storage units,
the detecting device comprising a measurement unit which measures a
current value at a time when a voltage difference between adjacent blocks
among the plurality of blocks becomes equal to a predetermined voltage,
and a detecting unit which detects abnormality of the electric storage
device based on a size of the measured current value.

[0012]According to various aspects of the present invention, abnormality
of the electric storage device can be detected based on a current value
at a predetermined time, with a small and simple structure and without
detecting pairs of current and voltage.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is an overall structural diagram of an abnormality detecting
device according to a preferred embodiment of the present invention.

[0014]FIG. 2 is a process flowchart of a preferred embodiment of the
present invention.

[0036]Preferred embodiments of the present invention will now be
described.

[0037]FIG. 1 shows a structure of an abnormality detecting device of a
battery pack in the present embodiment. The abnormality detecting device
is equipped in a hybrid automobile, similarly to the battery pack control
device shown in FIG. 14, and detects abnormality of the battery pack.
FIG. 1 does not show the battery power input and output section 1, the
vehicle control section 5, the engine control section 13, etc. which are
shown in FIG. 14, because these elements are similar to those in the
structure of FIG. 14. These elements will not be described again.

[0038]In FIG. 1, a battery pack 100 which is an electric storage device
comprises a plurality of blocks B1˜Bn, and the blocks B1˜Bn
are connected in series. Each block comprises one or a plurality of
single batteries connected in series. Each battery is, for example, a
nickel metal hydride battery or lithium-ion battery.

[0040]The comparators 140-1˜140-n compare the input block voltages
VB1˜VBn with a predetermined voltage, and determine whether or not
the block voltages VB1˜VBn have reached the predetermined voltage.
When the block voltages VB1˜VBn match the predetermined voltage,
the comparators 140-1˜140-On supply match signals to a determining
unit 160. The predetermined voltage for determination in each comparator
140-1˜140-n has the same value. Therefore, when the block voltages
VB1˜VBn are approximately equal, the match signals are output at an
approximately the same time from the comparators 140-1˜140-n. When,
on the other hand, the block voltages VB1˜VBn are not equal to each
other, the match signals are output from the comparators
140-1˜140-n at times corresponding to the values of the block
voltages. The match signals which are output from the comparators
140-1˜140n function as sampling signals for defining a time of
sampling of the current of the battery pack.

[0041]A current sensor 180 detects a current IB of the battery pack 100.
The detected current IB is supplied to the determining unit 160.

[0042]The determining unit 60 samples the current IB supplied from the
current sensor 180 at the times of the match signals supplied from the
comparators 140-1˜140-n, and stores the current values in a memory.
Therefore, the memory stores current values at times when the block
voltage VB1 of the block B1 has reached the predetermined voltage,
current values at times when the block voltage VB2 of the block B2 has
reached the predetermined voltage, . . . current values at times when the
block voltage VBn of the block Bn has reached the predetermined voltage.
The determining unit 160 applies a statistical process on the sampling
currents stored in the memory for each block, and sets a representative
current value of each block. For example, an average value may be
determined as the statistical process so that an average value of
sampling currents for block B1 is calculated and set as a representative
current value I1 of the block B1, an average value of the sampling
currents for the block B2 is calculated and set as a representative
current value I2 of the block b2, and an average value of the sampling
currents for the block Bn is calculated and set as a representative
current value In of the block Bn. The determining unit 160 also
determines, based on the representative current values I1˜In of the
blocks calculated in the above-described manner, whether or not an
abnormality has occurred in the battery pack 100 according to variation
of the representative current values I1˜In, and outputs the
determination result.

[0043]Note that while in the related art pair data of the block voltage
and the block current is detected, the IR of each block is calculated
through the method of least squares or through a regression analysis, and
the presence or absence of the abnormality is determined, in the present
embodiment, the presence or absence of abnormality is determined based on
the representative current values I1˜In of the blocks.

[0044]The determining unit 160 may be formed with a microcomputer, and may
be formed in an IC including the comparators 140-1˜140-n.

[0045]FIG. 2 is a flowchart of the abnormality determination process of
the present embodiment. First, a threshold voltage Vth which is the
predetermined voltage to be compared with the block voltages
VB1˜VBn in the comparators 140-1˜140-n is set (S101). The
method of setting the threshold voltage Vth is arbitrary, but it is
desirable that the threshold voltage Vth be set to a predetermined value
within a voltage change range when the battery pack 100 repeats charging
and discharging as the vehicle runs, in order to allow a large number of
current samplings in short period of time. The threshold voltage Vth may
be set as an absolute value or may be set based on a ratio with respect
to a reference SOC (state of charge) of the battery pack 100. The
threshold voltage Vth as the predetermined voltage may be supplied to the
comparators 140-1˜140-n in advance or a configuration may be
employed in which the threshold voltage Vth is registered in a register
and then supplied to the comparators 140-1˜140-n so that the
threshold voltage Vth can be suitably adjusted by replacing the content
of the register.

[0046]After the threshold voltage Vth is set (S101), the comparators
140-1˜140-n compare the block voltages VB1˜VBn to the
threshold voltage Vth, and current values when the block voltages
VB1˜VBn have reached the threshold voltage Vth are obtained (S102).
The obtained current value is sequentially stored in the memory for each
block. Then, for each block, a representative value of the current is
calculated (S103). The number of samples of the current to be obtained is
arbitrary, and may be fixed at a predetermined value. Alternatively, the
sampling time may be fixed. When the sampling time is fixed, there may be
cases where the number of samples differs among blocks. The number of
samples is at least two, and may be several tens. The representative
value of each block is, in general, the average value as described above,
but may alternatively be an intermediate value, a maximum value, or a
minimum value. It is desirable, however, that the representative value be
calculated based on the same standard for all blocks.

[0047]After the representative current value is calculated for each block,
it is determined whether or not abnormality has occurred based on a
degree of variation of the representative current value of each block
(S104). The determination result is supplied to the vehicle control
section similar to the related art, and the vehicle control section
controls the power input and output section of the battery pack 100 or
notifies the occupant of the vehicle of the abnormality of the battery
pack.

[0048]The process of FIG. 2 can be realized by the micro-computer which is
a part of the determining unit 160 or a part of the determining unit 160
and the comparators 140-1˜140-n sequentially executing an
abnormality diagnosis program stored in a ROM. The abnormality diagnosis
program may be stored on a recording medium such as a CD-ROM and
installed in a computer. Any type of recording medium for storage of the
abnormality diagnosis program may be used, and the recording medium may
be an arbitrary medium such as a CD-ROM, a DVD-ROM, a flash memory, etc.
The current value of each block obtained in S102 is sequentially stored
in a work memory of the micro-computer. In S103, the processor of the
micro-computer reads the plurality of current values for each block
stored in the memory, applies a predetermined statistical process, for
example, an average value calculation process, and calculates the
representative current value for each block. The calculated
representative current value is again stored in the work memory. In S104,
the processor of the micro-computer reads the representative current
value for each block stored in the work memory and calculates a
deviation. There exist several methods for calculation of the deviation.
For example, a minimum value and a maximum value of the representative
current values are extracted, and a difference is calculated or the
variance σ2 is calculated. Alternatively, the average of the
representative current values may be calculated and a maximum difference
value from the average value may be calculated. The calculated deviation
is compared in size with the threshold value stored in the working
memory, it is determined that an abnormality has occurred in a block
having a representative current value exceeding the threshold value, and
the determination result is output to the outside through an input and
output interface. As the determination result, in place of the presence
or absence of the abnormality, information for identifying the block in
which the abnormality has occurred may be output.

[0049]FIG. 3 shows a current sampling time for an arbitrary block Bi which
is a part of the battery pack 100. FIG. 3(a) shows a change with respect
to time of the block voltage detected by a voltage sensor 120-i. The
horizontal axis represents time (s) and the vertical axis represents a
voltage value (V). With repetition of charging and discharging, the block
voltage also changes between approximately 6 V and approximately 10 V.
FIG. 3 also shows the set threshold voltage Vth. In FIG. 3, the threshold
voltage Vth is set to approximately 7 V. In FIG. 3, the block voltage and
the threshold voltage Vth match at the times shown with black circles.

[0050]FIG. 3(b) shows a signal waveform of a result of comparison of the
block voltage and the threshold voltage Vth at the comparator 140-i. If a
configuration is employed in which the comparators 140-1˜140-n
compare the block voltages and the threshold voltage, and output a
voltage signal of a Hi level when block voltage≧threshold voltage
Vth, and output a voltage signal of a Low level when block
voltage<threshold voltage, a square wave signal as shown in FIG. 3 is
output. The times of the rise and fall of the square wave signal
represent times when the block voltage and the threshold voltage Vth are
equal. Therefore, the determining unit 160 samples, when the square wave
signal as shown in FIG. 3(b) is input, the current IB at times
synchronized with the the rise and fall of the square wave signal, so
that the current at the time when the block voltage has reached the
threshold voltage Vth can be obtained.

[0051]FIG. 3(c) shows a change with respect to time of the current
detected by the current sensor 180. With the repetition of the charging
and discharging, the current also changes to the positive side and the
negative side (when the positive side is set as the charging, the
negative side indicates discharging). The determining unit 160 samples
the current IB at the time of the rise and fall of the square wave signal
from the comparator 140-i and obtains I1˜I8. The obtained current
values are sequentially stored in the memory, and a representative value
of the current values I1˜I8 is calculated. The representative
current value for the block Bi is hereinafter referred to as IBi.

[0052]FIG. 4 is a diagram showing a plot of the representative current
value calculated for each block, with the vertical axis representing the
block voltage and the horizontal axis representing the current. Note that
while the current-voltage characteristic is used in the related art for
calculating the IR of each block, in the present embodiment, for the
representative value, the current value at the threshold voltage Vth
which is a particular voltage is plotted. In FIG. 4, the representative
current value IB1 of the block B1, the representative current value IB2
of the block B2, the representative current value IB3 of the block B3,
and the representative current value IBi of the block Bi are exemplified.
The slope of the current-voltage characteristic is IR, and because each
block has a unique IR, a straight line (or a curve) through the
representative current values plotted for each block can be considered.
In FIG. 4, a straight line through the plotted representative current
values is shown. In the related art, as shown in FIG. 12, a plurality of
pairs of current and voltage are detected and plotted, regression
analysis is applied to calculate a straight line 50, and the slope of the
straight line 50 is calculated as IR. The present embodiment, however,
simply considers a straight line through the representative current
values. The slope of the considered straight line would show the IR, but
a straight line is considered assuming that the straight line has a
predetermined slope. Then, based on the variation of the considered
straight lines and, fundamentally, the variation in the representative
current values of the blocks, the presence or absence of the abnormality
is determined.

[0053]The abnormality modes of the battery pack 100 may include, for
example, the followings:

[0056](3) increase of IR (due to elapse of lifespan and compromised
airtightness);

[0057](4) capacitance reduction; and

[0058](5) temperature increase.

[0059]Of these, in (1) self short-circuiting, the pole plates inside the
single battery (single cell) in the block contact each other and are
short-circuited, and thus the OCV (Open Circuit Voltage) is also reduced.
In the current-voltage characteristic, the intercept corresponding to the
OCV, which is a voltage value when the current is 0, is reduced. In FIG.
4, the straight lines 150 and the straight line 200 have the same slope,
but the intercept of the straight lines 150 and the intercept of the
straight line 200 differ significantly from each other. This is due to a
large variation between the representative current values IB1, IB2, and
IB2 and the representative current value IBi. In this case, it is
determined that the possibility that self short-circuiting has occurred
in the block Bi corresponding to the representative current value IBi is
high and that abnormality has occurred. More specifically, the variation
(deviation) is compared in size with a predetermined value, and when the
variation is less than or equal to the predetermined value, it is
determined as normal, and when the variation is greater than the
predetermined value, it is determined that abnormality has occurred. The
degree of variation of the representative current values may be evaluated
by an arbitrary evaluation equation. For example, the degree of variation
may be evaluated by comparing, in size, the variance σ2 with a
predetermined value, or may be evaluated by comparing, in size, a
difference between the maximum value and the minimum value of the
representative current value with a predetermined value.

[0060]In (2) minute short-circuiting, a metal deposit builds up inside the
battery and a conductive path is formed between positive and negative
poles, and the self discharge and internal discharge are increased. FIG.
5 shows a current-voltage characteristic for the case of the minute
short-circuiting. Because the voltage is reduced during discharge, the
voltage is reduced as shown with the straight line 300, compared to the
normal straight lines 150. In this case also, the reduction is due to a
large variation between the representative current values IB1, IB2, and
IB3 and the representative current value IBi, and it is determined that
the possibility that the minute short-circuiting has occurred in the
block Bi corresponding to the representative current value IBi is high
and that abnormality has occurred.

[0061]In (3) increase of IR, the slope of the current-voltage
characteristic is increased. FIG. 6 shows a current-voltage
characteristic for the case of increase in IR. The slope is increased as
shown with a straight line 400 with respect to the normal straight lines
150. This is also caused by the large variation between the
representative current values IB1, IB2, and IB3 and the representative
current value IBi, and it is determined that the possibility that the
increase in IR due to elapse of lifespan and compromising of airtightness
has occurred in the block Bi corresponding to the representative current
value IBi is high and that abnormality has occurred.

[0062]The (4) capacitance reduction is caused by repetition of the
charging and discharging, and similar to the case of (2) minute
short-circuiting, a characteristic as shown with a straight line 300 as
opposed to the normal straight lines 150 is observed as shown in FIG. 5.
This case also can be understood as having a large variation of the
representative current value IBi with respect to the representative
current values IB1, IB2, and IB3, and it is determined that the
possibility that the capacitance reduction has occurred in the block Bi
corresponding to the representative current value IBi is high and that
abnormality has occurred.

[0063]The (5) temperature increase occurs as a result of the (3) increase
of IR, and the slope is increased as shown with a straight line 400
compared to the normal straight lines 150, as shown in FIG. 6. This case
also can be understood as having a large variation of the representative
current value IBi with respect to the representative current values IB1,
IB2, and IB3, and it is determined that the possibility that the
temperature increase has occurred in the block Bi corresponding to the
representative current value IBi is high and that abnormality has
occurred.

[0064]As described, all of the abnormality modes of (1)-(5) can be
evaluated by the size of the variation (deviation) of the representative
current values IB1˜IBn of the blocks, and when the variation of the
representative current values IB1˜IBn is within a predetermined
range, no abnormality has occurred, and when the variation of the
representative current values B1˜Bn exceeds the predetermined
range, it is possible to determine that abnormality of any one of
(1)˜(5) has occurred in the block corresponding to the
representative current value exceeding the range. In the present
embodiment, the normal/abnormality is not determined by comparing the
representative current value of each block itself with the threshold
value, but rather, the normal/abnormality is determined based on the
variation of the representative current value. This is because it is
difficult to suitably set the threshold value for determining abnormality
because the electrochemical reaction of each block of the battery pack is
easily affected by the temperature and a change from an initial state may
occur in the block due to a memory effect, but it is difficult to
completely predict this change.

[0065]In the present embodiment, it is possible to easily and quickly
determine that abnormality of any of (1)-(5) has occurred based on the
degree of variation of the representative current values B1˜Bn of
the blocks, and to determine the block among the blocks B1˜Bn of
the battery pack 100 where the abnormality has occurred, but it is not
possible to identify which abnormality mode has occurred. Thus, it is
also possible to employ a configuration in which, after it is determined
that some abnormality has occurred, the type of abnormality is identified
with the use of other parameters.

[0066]In addition, in the present embodiment a battery is used as the
electric storage device, but the present embodiment can also be applied
to a capacitor as the electric storage device. As the abnormality mode of
the capacitor, of the above described abnormality modes (1)˜(5),
(4) capacitance reduction may occur. It is possible to compare the size
of a variation (deviation) of the representative current value of each
block forming a part of the capacitor with a predetermined range, and
when the variation is large and exceeds the predetermined range, to
determine that abnormality has occurred.

[0067]A preferred embodiment of the present invention has been described.
The present invention, however, is not limited to such a configuration
and various modifications may be made. A main point of the present
invention is that the abnormality is detected not using the pair of
current and voltage measured for each block, but based on the degree of
variation of current among blocks at a predetermined time for each block
(that is, a time when the voltage reaches a certain voltage), and
includes an arbitrary abnormality detection technique which
comprehensively uses other parameters in addition to the variation of the
current among blocks at the predetermined time for each block. In the
present embodiment, as the current at the predetermined time for each
block, the current is measured at a time when the voltage reaches a
certain voltage, but alternatively, it is also possible to employ a
configuration in which two or more threshold voltages are provided, and
the abnormality is comprehensively detected based on the variation of the
current among blocks at a time when the voltage reaches the first
threshold voltage for each block and based on the variation of the
current among blocks at a time when the voltage reaches the second
threshold voltage for each block. In other words, it is determined that
abnormality has occurred when both the variation of the current among
blocks at the time when the voltage has reached the first threshold value
for each block and the variation of the current among blocks when the
voltage has reached the second threshold value for each block exceed a
threshold value. Alternatively, it is possible to determine abnormality
when at least one of the variation of the current among blocks at the
time when the voltage has reached the first threshold voltage for each
block and the variation of the current among blocks at the time when the
voltage has reached the second threshold voltage for each block exceeds
the threshold value. The first and second threshold voltages may be
arbitrarily set, and, for example, the first threshold voltage may be set
as a threshold value at the discharge side and the second threshold
voltage may be set as a threshold value at the charge side.

[0068]An example configuration in which two threshold voltages are
provided and the abnormality is detected will now be described. When the
abnormality is detected with one set threshold voltage, it is not
possible to identify which of the abnormality modes (1)-(5) has occurred.
With the provision of two threshold voltages, it becomes possible to
identify which of the abnormality modes has occurred.

[0069]More specifically, in addition to the threshold voltage on the
discharge side, a threshold voltage on the charge side is set. The
threshold voltage on the discharge side is set as Vth1 and the threshold
voltage on the charge side of is set as Vth2. Currents at the times when
the voltage has reached the threshold voltages Vth1 and Vth2 are
detected, and degrees of variation are evaluated for the discharge side
and charge side. As the variation, a maximum value ΔI of the size
of the variation among representative current of the blocks, and a
variation ΔIdif=ΣIBj/n-IBi, of the block Bi in which the
variation is maximum, from an average value among blocks, are used. The
variations corresponding to the threshold voltage Vth1 of the discharge
side are set as ΔI1 and ΔIdif1 and the variations
corresponding to the threshold voltage Vth2 of the charge side are set as
ΔI2 and ΔIdif2. On both the discharge side and the charge
side, ΔI and ΔIdif are compared in size with the threshold
value, and presence or absence of abnormality and the abnormality mode
are identified.

[0070]FIG. 7 shows a current-voltage characteristic in the case of (1)
short-circuiting. FIG. 7 is similar to FIG. 4, but differs from FIG. 4 in
that a threshold voltage Vth2 is also set on the charge side (side of
positive current) and the current is detected for each block on the
charge side. When the discharge side is considered, if the absolute value
of the difference between IBi and IB3 among IB1˜IBn is the maximum,
ΔI1 is |IB3-IBi|, which is compared in size to the threshold value,
and it is determined that abnormality has occurred when the ΔI1
exceeds the threshold value. This applies similarly on the charge side,
and ΔI2=|IB3-IBi| which is compared in size with the threshold
value, and it is determined that abnormality has occurred when ΔI2
exceeds the threshold value. When ΔIdif is considered, from the
definition of ΔIdif, ΔIdif has a negative value when the
representative current value of the abnormal block Bi is larger than the
average current value of all blocks and has a positive value when the
representative current value of the abnormal block Bi is smaller than the
average current value. In FIG. 7, the representative current value IBi of
the abnormal block is at a more positive side than the normal blocks on
the discharge side, and thus, ΔIdif1 has a negative value.
Similarly, on the charge side ΔIdif2 has a negative value.

[0071]FIG. 8 shows a current-voltage characteristic in the case of
excessive discharge in the case of (2) minute short-circuiting and (4)
capacitance reduction. FIG. 8 is similar to FIG. 5 except that the
threshold voltage Vth2 is also set on the charge side, and the current is
detected for each block on the charge side. When the discharge side is
considered, ΔI1 exceeds the threshold value and the abnormality of
block Bi is detected, but ΔI2 is less than or equal to the
threshold value. In addition, ΔIdif1 has a negative value similar
to FIG. 7, but ΔIdif2 is within a normal range because the
ΔI2 is less than or equal to the threshold value.

[0072]FIG. 9 shows a current-voltage characteristic for the cases of (3)
IR increase, (5) temperature increase, and capacitance reduction of
capacitor. FIG. 9 is similar to FIG. 6 except that the threshold voltage
Vth2 is also set on the charge side and the current is detected for each
block on the charge side. On the discharge side, ΔI1 exceeds the
threshold value and abnormality of the block Bi is detected, and
ΔIdif1 has a negative value. On the charge side, on the other hand,
ΔI2 also exceeds the threshold value and abnormality in the block
Bi is detected, and, because IBi is shifted to the negative side,
ΔIdif2 has a positive value. In other words, signs of ΔIdif1
and ΔIdif2 have opposite polarities.

[0073]FIG. 10 shows a current-voltage characteristic for the case of
capacitance reduction and excessive charging. Similar to FIGS. 7-9, the
threshold voltage Vth2 is set also on the side of the charge, in addition
to the threshold voltage Vth1 on the discharge side. Reference numeral
500 represents a characteristic of the block Bi. On the discharge side,
ΔI1 is less than or equal to the threshold value and is normal, but
ΔI2 exceeds the threshold value and abnormality in the block Bi is
detected. In addition, on the charge side, because IBi is shifted to the
negative side, ΔIdif2 has a positive value.

[0074]Because the signs of ΔIdif1 and ΔIdif2 change according
to the abnormality mode, the abnormality mode can be identified based on
the change in the signs. FIG. 11 summarizes the result of comparison in
size of ΔIl, ΔI2, ΔIdif1, and ΔIdif2 with the
threshold value A. In FIG. 11, for example, when ΔI1 exceeds the
threshold value A (YES) and the ΔI2 also exceeds the threshold
value A (YES), if the sign of ΔIdif1 is negative, that is,
ΔIdif<-A and the sign of ΔIdif2 is negative, that is,
ΔIdif2<-A, it is determined that short-circuiting as shown in
FIG. 7 has occurred. When, on the other hand, ΔI1 and ΔI2
exceed the threshold value, but the sign of ΔIdif1 is negative and
the sign of ΔIdif2 is positive, that is, ΔIdif>A, it is
determined that the IR increase, temperature increase, or capacitance
reduction of the capacitor as shown in FIG. 9 has occurred. When, on the
other hand, only ΔI1 exceeds the threshold value and ΔI2 is
within the normal range, it is determined that excessive discharge has
occurred due to the minute short-circuiting or the capacitance reduction
as shown in FIG. 8. When only ΔI2 exceeds the threshold value and
ΔI1 is within the normal range, it is determined that excessive
charge state has occurred due to capacitance reduction shown in FIG. 10.
Although the same value A is used for the threshold values of ΔI1,
ΔI2, ΔIdif1, and ΔIdif2, it is also possible to employ
different values depending on the malfunctions to be detected.

[0075]A person with ordinary skill in the art can think of various
algorithms for identifying the abnormality mode by referring to FIG. 11.
The present embodiment includes arbitrary algorithms for identifying the
abnormality mode by combining ΔI2, ΔI2, ΔIdif1, and
ΔIdif2. As is clear from FIG. 11, it is also possible to identify
the abnormality mode based only on ΔIdif1 and ΔIdif2 without
the use of ΔI1 and ΔI2.

[0076]In the present embodiment, a current value is obtained for each
block at time when the voltage of the block becomes equal to a
predetermined voltage. More specifically, the current values are obtained
in S102 of FIG. 2 at times when the block voltages VB1˜VBn have
reached the threshold voltage Vth. The current value at the time of
reaching the threshold voltage Vth does not require a strict
simultaneity, and may be obtained within a certain allowable time range.
Simultaneity within 100 msec would be sufficient for the simultaneity
required for determining the abnormality of an electric storage battery.
The allowable range of the simultaneity would be determined according to
the precision required for the abnormality determination of the electric
storage battery. When the electric storage battery is equipped in a
hybrid vehicle, the drive carrier frequency of the hybrid motor is in the
order of KHz, and according to Nyquist's theorem, theoretically,
simultaneity of 1 msec or less is desired. Based on the experiences of
the present inventors, however, the simultaneity of such a degree is not
required, and the simultaneity of approximately 100 msec as described
above is sufficient. It is also possible to set the allowable range of
simultaneity from the viewpoint of securing precision necessary for
reliably determining an abnormality mode having the highest priority
among various abnormality modes of the electric storage battery. For
example, when priority for the IR increase is particularly high among the
abnormality modes, it is possible to set simultaneity necessary for
reliably detecting an increase of IR of a predetermined amount or greater
(for example, an amount of change ΔIR=10% compared to the normal
value).

[0077]In addition, in the present embodiment, the representative value of
each block is calculated in S103 of FIG. 2, but it is also possible to
calculate the representative value while removing a current value sample
having a low precision when the representative value of each block is
calculated, to improve the precision of the simultaneity. More
specifically, it is determined whether or not the current value sample is
to be included using a distribution of the current values for each block.
More specifically, a configuration may be employed in which (a) a current
value sample having a deviation of the current value which is larger, by
a predetermined value or greater, than the distribution of the current
values is removed from the samples for calculating the representative
value, (b) the representative value itself is not calculated when the
deviation of the current value distribution itself is large, etc. The
condition of (b) can also be described in other words as calculating the
representative value only when the deviation of the current value
distribution itself is less than or equal to the predetermined value.
FIG. 15 shows a simulation result showing a relationship between the
precision of simultaneity and the current value distribution. FIG. 16
shows a current profile used in the simulation. In FIG. 15, current
distributions are shown for times when there is no delay with respect to
the time when the block voltage has reached the threshold voltage Vth (no
delay), the delay is 10 msec, the delay is 50 msec, the delay is 100
msec, and the delay is 1 sec. While the distribution with the time with
no delay has a standard deviation of 1.83 and variance of 3.35, the
distribution with the delay of 1 sec has a standard deviation of 13.00
and a variance of 168.88, and thus the distribution is increased as the
precision of simultaneity is reduced. By removing the current value
samples using one of (a) or (b) described above, it is possible to
improve the precision of the representative value of each block, that is,
the precision of the simultaneity, in a simple manner, that is, without
increasing the processing capability of the hardware. With such a
configuration, the precision of the abnormality determination can be
improved.

[0078]Specifically, the current at the time when the block voltage has
reached the threshold voltage Vth can be sequentially stored by supplying
outputs from the comparators 140-1 or the like in FIG. 1 to the
determining unit 160, capturing the comparator output and the current
value from the current sensor 180 at the determining unit 160 into a
register, and transferring the current value stored in the register to
the memory at the time when the comparator output changes. The comparator
output may have, for example, 8 bits, and it is determined whether or not
a previous value and the current value match. When the previous value and
the current value do not match, it is determined that the comparator
output has changed, that is, the block voltage has reached the threshold
voltage Vth. In a strict sense, the current value at the timing when the
comparator output has changed may be any time of immediately before the
comparator output changes or immediately after the comparator output
changes, or may be an average value of current values at the time
immediately before the comparator output changes and the time immediately
after the comparator output changes. In any case, it is sufficient that
the simultaneity within the allowable range be secured, as described
above.

[0079]In the present embodiment, the abnormality of the battery pack 100
is detected based on the current at the time when the block voltage has
reached the threshold voltage Vth. Alternatively, it is also possible to
detect the abnormality of the battery pack 100 based on a voltage
difference between adjacent blocks rather than the block voltage of each
block.

[0080]FIG. 17 shows a structure when the abnormality of the battery pack
100 is detected based on the voltage difference between adjacent blocks.
A detected voltage VB1 from a voltage sensor 120-1 which detects the
voltage of the block B1 and a detected voltage VB2 from a voltage sensor
120-2 which detects a voltage of the block B2 which is adjacent to the
block B1 are both supplied to a subtractor 130-1. The subtractor 130-1
calculates a voltage difference VB1-VB2 between the block B1 and the
block B2, and supplies the voltage difference to a comparator 140-1. The
subtractor 130-1 may calculate VB2-VB1 as the voltage difference between
adjacent blocks or may alternatively calculate VB1-VB2 or an absolute
value of VB2-VB1. The comparator 140-1 compares the voltage difference
supplied from the subtractor 130-1 with a predetermined threshold value
VTH, and determines whether or not the voltage difference matches the
predetermined threshold value VTH. Then, the comparator 140-1 supplies a
match signal to a determining unit 160 at the time when the voltage
difference matches the predetermined threshold value VTH. A plurality of
subtractors 130-1 and comparators 140-1 are provided. The match signal
supplied from the comparator 140-1 to the determining unit 160 functions
as a sampling signal which defines a time when the current of the battery
pack 100 is sampled.

[0081]FIG. 18 shows another configuration when the abnormality of the
battery pack 100 is detected based on the voltage difference between
adjacent blocks. A detected voltage from a voltage sensor 120-1 which
detects the voltage of the block B1 and a detected voltage VB2 from a
voltage sensor 120-2 which detects the voltage of the block B2 adjacent
to the block B1 are both supplied to a subtractor 130-1. In addition, the
detected voltage VB2 from the voltage sensor 120-2 which detects the
voltage of the block B2 is also branched and supplied to a subtractor
130-2. In addition, a detected voltage VB3 from a voltage sensor 120-3
which detects the voltage of the block B3 adjacent to the block B2 is
supplied to the subtractor 130-2. The subtractor 130-1 calculates a
voltage difference between the voltage VB1 and the voltage VB2, and
supplies the voltage difference to a comparator 140-1. The subtractor
130-2 calculates a voltage difference between the voltage VB2 and the
voltage VB3 and supplies the voltage difference to a comparator 140-2.
The comparator 140-1 compares the voltage difference supplied from the
subtractor 130-1 with a predetermined threshold value VTH, and determines
whether or not the voltage difference matches the predetermined threshold
value VTH. Then, the comparator 140-1 supplies a match signal to the
determining unit 160 at a time when the voltage difference matches the
threshold value VTH. Similarly, the comparator 140-2 compares the voltage
difference supplied from the subtractor 130-2 with the predetermined
threshold value VTH and determines whether or not the voltage difference
matches the predetermined threshold value VTH. Then, the comparator 140-2
supplies a match signal to the determining unit 160 at a time when the
voltage difference matches the threshold value VTH. In this
configuration, if abnormality occurs in the block B2, for example, the
abnormality affects not only the voltage difference calculated by the
subtractor 130-1, but also the voltage difference calculated by the
subtractor 130-2.

[0082]FIG. 19 shows a result (characteristic diagram showing a
relationship between current and voltage difference) of sampling a
current value at a time when the voltage difference between adjacent
blocks has reached the predetermined threshold value VTH. In FIG. 19, the
horizontal axis represents the current value and the vertical axis
represents the voltage difference. When the battery pack 100 is normal,
as shown in FIG. 19, the voltage difference is a straight line through 0,
and the values (absolute values) of current values I1 and I2 at the time
when the voltage difference matches the threshold value VTH is greater
than a reference current value Iref.

[0083]FIG. 20 shows a characteristic diagram when the self
short-circuiting occurs in the battery pack 100. As shown in FIG. 4, when
self short-circuiting occurs, because the straight lines 150 and the
straight line 200 have the same gradient, the voltage difference becomes
approximately constant, the current values at the time when the voltage
difference matches the threshold value VTH are detected as I1, I2, I3,
I4, I5, etc., and a current value having a smaller absolute value to the
reference current value Iref is detected.

[0084]FIG. 21 shows a characteristic diagram when the minute
short-circuiting occurs in the battery pack 100. As shown in FIG. 5, when
the minute short-circuiting occurs, because the voltage during discharge
is reduced, the voltage difference has a characteristic of gradually
increasing to the discharge side. The current value at the time when the
voltage difference matches the threshold value VTH is detected as I1
(discharge side), and a current value I1 having a smaller absolute value
than the reference current value Iref is detected.

[0085]FIG. 22 shows a characteristic diagram when the IR increase occurs
in the battery pack 100. As shown in FIG. 6, when the IR increase occurs,
the slope is increased, such as the straight line 400 compared to the
normal straight lines 150. The voltage difference is a straight line
passing through 0 similar to the normal case, but the slope is increased
due to the IR increase. Thus, the absolute values of the current values
I1 and I2 at the time when the voltage difference matches the threshold
value VTH are gradually reduced. In other words, the degree of the IR
increase can be evaluated based on the absolute values of the current
values I1 and I2.

[0086]FIG. 23 shows a characteristic diagram when a capacitance reduction
(excessive charge) occurs in the battery pack 100. As shown in FIG. 10,
when the capacitance reduction (excessive charge) occurs, the voltage is
increased on the charge side, and thus in the characteristic, the voltage
difference gradually increases on the charge side. The current value at
the time when the voltage difference matches the threshold value VTH is
detected as I1 (charge side), and a current value I1 having a smaller
absolute value than the reference current value Iref is detected.

[0087]As described, the size of the current value (absolute value) at the
time when the voltage difference matches the threshold value VTH and the
reference current value Iref are compared in size, and when the absolute
value of the detected current value is larger than the reference current
value Iref, it is determined that the battery pack 100 is normal, and
when the absolute value of the detected current value is smaller than the
reference voltage value Iref, it is determined that abnormality has
occurred in the battery pack 100. In addition, even when the absolute
value of the detected current value is greater than the reference current
value Iref, if the value is small (that is, the value is close to the
reference current value), it is possible to determine that the internal
resistance is increasing.

[0088]With the circuit structure of FIG. 17, it is not possible, even when
abnormality has occurred in the block B2, for example, to determine in
which of the blocks B1 and B2 the abnormality has occurred. However, with
the structure of FIG. 18, because the voltage difference VB2-VB3 is
calculated in addition to the voltage difference VB1-VB2, it is possible
to determine that the abnormality has occurred in the block B2, instead
of the block B1.

[0089]As described, the abnormality of the battery pack 100 can be
detected by detecting a current value at a time when the voltage
difference between adjacent blocks has reached a predetermined threshold
value VTH, and comparing in size the current value with the reference
current value Iref. In FIGS. 19-23, VB1-VB2 or the like is used as the
voltage difference, but it is also possible to use the absolute value.
When the voltage difference between adjacent blocks is used, a circuit
for detecting a voltage difference would be newly required. However, when
the battery pack 100 is equipped in a hybrid vehicle as a lithium-ion
battery, a structure is employed in which a plurality of blocks are
managed with a single IC, and thus it is possible to provide the voltage
difference detecting circuit inside the IC.